The present invention relates to pulse combustion burners and, more particularly, to a high flow capacity feed valve for use in self-feeding one or more components of a combustible gaseous mixture into the burner.
In pulse combustion burners of the Helmholtz type, an oscillating or pulsed flow of combustion gases through the burner is maintained at a frequency determined by burner geometry and fuel supply characteristics, including the mixing of the fuel components. Typically, a combustion chamber of a given size cooperates with a tailpipe or exhaust pipe of specific dimensions to provide explosive combustion cycles, thermal expansion of the gaseous products of combustion, and oscillating gas pressures which provide the pulsed flow of combustion products through the burner. In order to make the pulse combustion process self-substaining, the oscillating gas pressure may be used to provide self-feeding of components of a combustible gaseous mixture which generally comprises air and a gaseous fuel such as natural gas.
It is known to use one-way flapper valves to self-feed air and/or fuel gas to a pulse burner. Such flapper valves include a flexible flapper or diaphragm movably mounted between a valve plate having valve flow openings therein and a backer plate arranged to limit the movement or stroke of the flapper. The flapper is arranged to move between a closed position overlying the valve openings and an opened position adjacent the backer plate in response to the fluid pressures on opposite sides of the flapper. In pulse burner applications, the valve openings and flapper are sized to assure movement in response to the oscillating operating pressures and adequate flow through the valve.
The use of flapper valves has not been entirely satisfactory since they are relatively large valves and tend to interfere with burner applications requiring placement of the burner apparatus in a particular mounting location or an enclosed cabinet. Generally, the air flapper valve will be larger and more troublesome since the ratio of air to natural gas is about 12:1 in most combustion processes.
In higher fuel input burner applications, for example, in the range of 100,000 BTU/hr. or more, the increased size of the flapper valve also makes it more difficult to operate with the prevailing burner pressures and desired frequencies which may range from 10 hertz to several hundred hertz. More particularly, as the flapper valve flow openings increase in size and number, it becomes increasingly more difficult to start and stop the flapper movement as it is biased between its opened and closed position using the oscillating burner pressures. For these reasons, the valve plate is typically provided with one or more circular arrays of valve openings which are engaged by annular shaped flappers retained in aligned position by the backer plate. The flow capacity of the valve is determined by the lesser of the total area of the valve openings or, in adjustable valves, the flow area of the circumferential band or opening between the valve plate and the flapper in its opened position. The flow capacity of the latter valve may be varied by adjustment of the flapper stroke.
The adjustment of the input rate to the burner is more difficult for larger sized flapper valves since small changes in the distance between the valve plate and opened flapper as determined by the spacing of the backer plate result in substantial flow variations. In such cases, the backer plate is adjustably mounted to the valve plate in order to enable variation of the flapper movement or stroke. Accordingly, as the overall diameter of the plates is increased for larger input applications, a given change in plate spacing results in a greater change in flow.
Burner applications in the range of a 1,000,000 BTU/hr. input and more present extreme flapper valve strength requirements. The valve and backer plates must be reinforced by intergral web-type arrangements to resist flexing and stress failure due to exposure to the cyclic pulse burner pressure loads. The cost of the flapper valve is significantly increased by the additional reinforcement required in such applications.